1. Technical Field of the Invention
The present invention is directed to systems, devices, and methods for improving noise reduction in multi-party telephone systems.
2. Description of Related Art
As technology proceeds into the twenty-first century, electronic communication methods grow exceedingly important in allowing efficient, inexpensive transfer of information. In particular, multi-party conferencing for a telecommunications system allows several individuals in different locations to participate in group discussions via, for example, conference bridges. Within a multi-party bridge, the incoming microphone signals from the different parties are digitally mixed and transmitted to the respective loudspeakers of the different parties. An alternative approach is to send all microphone signals of the respective users.
A major problem posed by multi-party telecommunication, systems, however, is the attenuation of background noise in the transmitted signal. This noise may be caused by either disturbance from the external environment, or internal noise produced within the system (i.e., talker and listener echoes). Prior implementations of multi-party bridges attempt to resolve this issue by only mixing the incoming signals from a fixed subset of the parties. This choice, however, is typically performed on the basis of signal level and speaker activity of the different parties, where the most recent active talkers are retained if no speaker activity is present from any other party. Although this solution reduces external background noise, it still poses the problem of re-transmission, in which the microphone re-transmits audio signals produced by the speaker, resulting in echoes and sustained feedback oscillations.
Previous methods of echo suppression include disabling, or substantially attenuating, one of the respective send and receive telecommunication channels in favor of the other. This approach, however, often results in undesirable clipping of voice signals during a conversation. Additionally, background noises are often completely muted during pauses in the conversation, such that a user may perceive it as a disconnected call.
In view of the current state of the art, as described above, a modification to the basic operation of mixing incoming signals from a fixed subset of parties is needed, such that the microphone signal coming from a first party A (or a number of parties) may be excluded from the sum of the signals transmitted back to party A (or to the number of parties). One reason for this is that the microphone signal from A may already be present in the loudspeaker of a talking party A (due to the side-tone in the telephone set), and that, if a significant transmission delay is present in the system, the microphone signal will be perceived as an undesirable echo.
There is therefore a need for improved techniques for noise reduction in multi-party telephone systems.
A method, system, and apparatus are provided, such that cross talk terms may be removed from speech signals in a multi-party conference system, having a plurality of users. This is accomplished by first estimating the respective cross talk terms for each of the said plurality of users. These terms are then used for controlling the transmission of speech and audio signals between the users. In one approach, the transmission input speech signals are multiplied by time varying scalars, e.g., taking the values 0 and 1 (on and off), thereby controlling the acoustic cross talk terms. In another approach, line cross talk terms are inverted and multiplied to input speech signals, in effect filtering the input speech signals, such that respective source speech signals may be recovered from said plurality of multi-party conference users.
In the case of separation of sources, the signals are separate; thus original speech signals are not recovered. Instead, signals are filtered versions and not identical to the corresponding source speech signals.